Charge air cooler condensate purging cycle

ABSTRACT

Methods and systems are provided for purging condensate from a charge air cooler to an engine intake. During an engine deceleration event, the vehicle is downshifted into a lower gear to increase RPM and airflow through a charge air cooler to purge stored condensate to the engine intake. By delivering condensate while an engine is not fueled, misfire events resulting from ingestion of water are reduced.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/648,854, entitled “CHARGE AIR COOLER CONDENSATE PURGINGCYCLE,” filed on Oct. 10, 2012, now U.S. Pat. No. 8,961,368, the entirecontents of which are hereby incorporated by reference for all purposes.

BACKGROUND/SUMMARY

Engines may increase output power by using boosting devices thatcompress intake air. Since charge compression increases air temperature,charge air coolers may be utilized downstream of a compressor to coolthe compressed air, further increasing the potential power output of theengine. As intake air passes through the charge air cooler and is cooledbelow a dew point, condensation occurs. The condensate may beaccumulated at a trap and delivered to the engine subsequently, e.g.,during steady-state or cruise conditions, at a controlled rate ofingestion. However, because the ingested water slows the rate ofcombustion, even small errors in the introduction of water into theengine can increase the likelihood of misfire events. Engine controlsystems may employ various misfire control approaches to reduce misfirescaused by the ingestion of water.

One example approach for addressing moisture induced misfires is shownby Tonetti et al. in EP 1607606. Therein, an intake air flow rate isadjusted based on an oxygen concentration of recirculated exhaust gas tocompensate for condensate in the EGR. Another example approach is shownby Wong et al. in U.S. Pat. No. 6,748,475. Therein, a fuel injection andspark timing is adjusted based on a parameter indicative of an oxygenconcentration or water concentration of recirculated exhaust gas. Thisallows misfire events arising during steady-state conditions due to asudden ingestion of too much water or condensate to be reduced. Evenwhen the amount of water ingested is small, during a transient tip-infrom steady state conditions, such as when going from low to moderateair mass flow rates to high air mass flow rates, the ingested water cancause slow combustion issues. In particular, the high air mass flow ratecan break the surface tension of the condensate, and release from thecharge air cooler where the engine ingests it in larger quantities.

However, the inventors herein have identified potential issues with suchan approach. As one example, even with adjustments to intake air flowrate, fuel injection, and/or spark timing, misfires caused due tocondensate ingestion during steady-state conditions may not besufficiently addressed. Specifically, engine combustion stability duringsteady-state conditions may be sensitive to the amount of condensate.Consequently, even small errors in condensate metering can lead tomisfires.

In one example, some of the above issues may be addressed by a methodfor a boosted engine comprising: downshifting a transmission gear toincrease engine speed and increase engine airflow (air mass flow rate)in response to a deceleration event and a condensate level in a chargeair cooler (CAC). The method may further include, increasing an openingof an intake throttle to increase airflow through the charge air cooler.In this way, condensate can be purged efficiently without incurringmisfire events.

As one example, an engine controller may downshift a transmission gearto initiate delivery of condensate collected at a CAC to an engineduring a deceleration event. For example, in response to a tip-out, whenthe engine is spinning un-fueled (e.g., during a deceleration fuel shutoff or DFSO event), the vehicle may be downshifted from a transmissionthird gear to a transmission second gear to increase engine speed andmanifold vacuum. Then, condensate may be pulled into the engine from theCAC. Additionally or optionally, an intake throttle may be opened toincrease airflow to the engine and through the CAC. By opening thethrottle during the deceleration, intake manifold vacuum generated fromthe spinning engine may be increased and used to increase purgingefficiency.

In this way, by delivering condensate from a CAC to an engine during adeceleration event, the large amount of intake manifold vacuum generatedfrom downshifting can be advantageously used to draw condensate into theengine. By delivering the condensate to the engine during conditionswhen cylinder combustion is not occurring, the condensate can passthrough the engine system without degrading combustion stability.Further, since the condensate is introduced while no combustion isoccurring, concurrent engine actuator adjustments for misfire controlmay not be required. Overall, a larger amount of condensate may bepurged into the engine without increasing engine misfires.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example engine system including acharge air cooler.

FIGS. 2A-B and 3A-B show example embodiments of a valve coupled to thecharge air cooler for delivering condensate from the charge air coolerto an engine intake.

FIG. 4 shows a high level flow chart of a method for purging charge aircooler condensate to an engine intake during an engine decelerationevent.

FIG. 5 shows a flow chart illustrating a method for inferring acondensate level at the charge air cooler.

FIG. 6 shows a flow chart illustrating a method for purging CACcondensate to an engine intake during a deceleration event bydownshifting a transmission gear and/or increasing airflow through aCAC.

FIGS. 7-8 show example condensate purging operations.

DETAILED DESCRIPTION

The following description relates to systems and methods for purgingcondensate from a charge air cooler (CAC) coupled to an engine system,such as the system of FIG. 1. Condensate purging may be performedopportunistically, during engine deceleration events when fueling of anengine cylinder is temporarily stopped, such as during a tip-outcondition. Purging may be initiated during a deceleration event bydownshifting a transmission gear to increase engine speed and manifoldvacuum, drawing condensate from the CAC into the engine. Alternatively,if a lower gear is unavailable, condensate purging may be initiated byincreasing airflow though the CAC. An engine controller may beconfigured to perform a control routine, such as the routine of FIG. 4,to open a valve coupled to the charge air cooler (FIGS. 2A-B and 3A-B)during a deceleration fuel shut off event to purge condensate to theengine intake during conditions when no cylinder combustion isoccurring. Purge settings may be based on an amount of condensate storedat the CAC, as inferred from a model described at FIG. 5. During enginedeceleration, an intake throttle opening may be temporarily increased toincrease an intake air flow to the engine, further assisting in drawingthe condensate into the engine. Additionally, condensate may be drawninto the engine from the CAC by downshifting a transmission gear toincrease engine speed. An example control routine for purging CACcondensate to an engine intake during a deceleration event is shown atFIG. 6. Example purging operations are shown at FIGS. 7-8. In this way,condensate can be purged from a CAC during conditions when misfireevents due to water ingestion are not likely.

FIG. 1 is a schematic diagram showing an example engine 10, which may beincluded in a propulsion system of an automobile. The engine 10 is shownwith four cylinders 30. However, other numbers of cylinders may be usedin accordance with the current disclosure. Engine 10 may be controlledat least partially by a control system including controller 12, and byinput from a vehicle operator 132 via an input device 130. In thisexample, input device 130 includes an accelerator pedal and a pedalposition sensor 134 for generating a proportional pedal position signalPP. Each combustion chamber (e.g., cylinder) 30 of engine 10 may includecombustion chamber walls with a piston (not shown) positioned therein.The pistons may be coupled to a crankshaft 40 so that reciprocatingmotion of the piston is translated into rotational motion of thecrankshaft. Crankshaft 40 may be coupled to at least one drive wheel ofa vehicle via an intermediate transmission system 150. Further, astarter motor may be coupled to crankshaft 40 via a flywheel to enable astarting operation of engine 10.

An engine output torque may be transmitted to a torque converter (notshown) to drive the automatic transmission system 150. Further, one ormore clutches may be engaged, including forward clutch 154, to propelthe automobile. In one example, the torque converter may be referred toas a component of the transmission system 150. Further, transmissionsystem 150 may include a plurality of gear clutches 152 that may beengaged as needed to activate a plurality of fixed transmission gearratios. Specifically, by adjusting the engagement of the plurality ofgear clutches 152, the transmission may be shifted between a higher gear(that is, a gear with a lower gear ratio) and a lower gear (that is, agear with a higher gear ratio). As such, the gear ratio differenceenables a lower torque multiplication across the transmission when inthe higher gear while enabling a higher torque multiplication across thetransmission when in the lower gear. The vehicle may have four availablegears, where transmission gear four (transmission fourth gear) is thehighest available gear and transmission gear one (transmission firstgear) is the lowest available gear. In other embodiments, the vehiclemay have more or less than four available gears. As elaborated herein, acontroller may vary the transmission gear (e.g., upshift or downshiftthe transmission gear) to adjust an amount of torque conveyed across thetransmission and torque converter to vehicle wheels 156 (that is, anengine shaft output torque).

Vehicle speed may be reduced by engaging vehicle brakes (e.g., wheelbrakes). Vehicle speed may be further reduced through engine braking. Insome examples, engine braking may be utilized to slow the vehicleinstead of wheel brakes. In this way, the use of wheel brakes may bereduced, increasing their lifespan. Engine braking may occur during atip-out (e.g., deceleration event) when the engine spins, un-fueled. Thecontroller may vary a transmission gear based on driving conditions,such as the deceleration event. For example, in response to a tip-out,when the engine is spinning un-fueled (e.g., during a deceleration fuelshut off or DFSO event) the vehicle may require engine braking in orderto increase deceleration. By downshifting to a lower transmission gear,engine braking may be increased. As the transmission shifts to a lowergear, the engine speed (Ne or RPM) increases, increasing engine airflow.An intake manifold vacuum generated by the spinning engine may beincreased at the higher RPM. As engine braking increases, a vehiclecontrol system may coordinate and adjust the braking efforts ofalternative vehicle brakes, such as the wheel brakes, to maintain adesired deceleration rate. For example, while the engine braking istemporarily increased, a wheel braking effort may be temporarilydecreased.

However, if an air intake throttle is opened, such as during a CACpurging cycle, the vehicle may not receive the desired engine braking.In one example, alternative brakes (e.g., wheel brakes) may be appliedto maintain a desired deceleration rate typically present during enginebraking (when the throttle is closed). In another example, where theengine or drive-train is coupled to an electric machine (e.g., in ahybrid electric vehicle) or any other hybrid-like device (hydraulic orpneumatic), the throttle opening and transmission downshifting may becoordinated with such devices (e.g., the devices could be operated in anenergy or torque absorbing mode) to maintain the desired decelerationrate while keeping engine speed and mass flow rate high (to continuepurging the condensate during the deceleration). In this way, thecontroller may increase wheel brake torque, motor torque, or othertorque-absorbing means while the throttle is open to maintain a desireddeceleration rate.

Combustion chambers 30 may receive intake air from intake manifold 44via intake passage 42 and may exhaust combustion gases via exhaustmanifold 46 to exhaust passage 48. Intake manifold 44 and exhaustmanifold 46 can selectively communicate with combustion chamber 30 viarespective intake valves and exhaust valves (not shown). In someembodiments, combustion chamber 30 may include two or more intake valvesand/or two or more exhaust valves.

Fuel injectors 50 are shown coupled directly to combustion chamber 30for injecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12. In this manner, fuel injector 50provides what is known as direct injection of fuel into combustionchamber 30; however it will be appreciated that port injection is alsopossible. Fuel may be delivered to fuel injector 50 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail.

Intake passage 42 may include throttle 21 having a throttle plate 22 toregulate air flow to the intake manifold. In this particular example,the position (TP) of throttle plate 22 may be varied by controller 12 toenable electronic throttle control (ETC). In this manner, throttle 21may be operated to vary the intake air provided to combustion chamber 30among other engine cylinders. In some embodiments, additional throttlesmay be present in intake passage 42, such as a throttle upstream of thecompressor 60 (not shown).

Further, in the disclosed embodiments, an exhaust gas recirculation(EGR) system may route a desired portion of exhaust gas from exhaustpassage 48 to intake passage 42 via EGR passage 140. The amount of EGRprovided to intake passage 42 may be varied by controller 12 via EGRvalve 142. Under some conditions, the EGR system may be used to regulatethe temperature of the air and fuel mixture within the combustionchamber. FIG. 1 shows a high pressure EGR system where EGR is routedfrom upstream of a turbine of a turbocharger to downstream of acompressor of a turbocharger. In other embodiments, the engine mayadditionally or alternatively include a low pressure EGR system whereEGR is routed from downstream of a turbine of a turbocharger to upstreamof a compressor of the turbocharger. When operable, the EGR system mayinduce the formation of condensate from the compressed air, particularlywhen the compressed air is cooled by the charge air cooler, as describedin more detail below.

Engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 60 arrangedalong intake manifold 44. For a turbocharger, compressor 60 may be atleast partially driven by a turbine 62, via, for example a shaft, orother coupling arrangement. The turbine 62 may be arranged along exhaustpassage 48. Various arrangements may be provided to drive thecompressor. For a supercharger, compressor 60 may be at least partiallydriven by the engine and/or an electric machine, and may not include aturbine. Thus, the amount of compression provided to one or morecylinders of the engine via a turbocharger or supercharger may be variedby controller 12.

Further, exhaust passage 48 may include wastegate 26 for divertingexhaust gas away from turbine 62. Additionally, intake passage 42 mayinclude a compressor recirculation valve (CRV) 27 configured to divertintake air around compressor 60. Wastegate 26 and/or CRV 27 may becontrolled by controller 12 to be opened when a lower boost pressure isdesired, for example.

Intake passage 42 may further include charge air cooler (CAC) 80 (e.g.,an intercooler) to decrease the temperature of the turbocharged orsupercharged intake gases. In some embodiments, charge air cooler 80 maybe an air to air heat exchanger. In other embodiments, charge air cooler80 may be an air to liquid heat exchanger. CAC 80 may be a variablevolume CAC, such as shown in the embodiments of FIGS. 2A-B and 3A-B. Inthose embodiments, as described in more detail below, the charge aircooler 80 may include a valve to selectively modulate the amount andflow velocity of intake air traveling through the charge air cooler 80in response to condensation formation within the charge air cooler aswell as engine load conditions.

Hot charge air from the compressor 60 enters the inlet of the CAC 80,cools as it travels through the CAC, and then exits to enter the engineintake manifold 44. Ambient air flow from outside the vehicle may enterengine 10 through a vehicle front end and pass across the CAC, to aid incooling the charge air. Condensate may form and accumulate in the CACwhen the ambient air temperature decreases, or during humid or rainyweather conditions, where the charge air is cooled below the water dewpoint. When the charge air includes recirculated exhaust gasses, thecondensate can become acidic and corrode the CAC housing. The corrosioncan lead to leaks between the air charge, the atmosphere, and possiblythe coolant in the case of water-to-air coolers. To reduce theaccumulation of condensate and risk of corrosion, condensate may becollected at the bottom of the CAC, and then be opportunistically purgedinto the engine during selected engine operating conditions, such asduring acceleration or deceleration events. However, if the condensateis introduced at once into the engine during an acceleration event, itmay increase the chance of engine misfire due to the ingestion of water.

Thus, as elaborated herein with reference to FIGS. 4-8, condensate maybe purged from the CAC to the engine during conditions when the engineis not being fueled, such as during a DFSO event (fuel injection toengine cylinders is shut off). This purging during a DFSO may allowcondensate to be delivered to the engine without causing misfire events.In one example, condensate purging during a DFSO may be initiated bydownshifting a transmission gear with a concomitant opening of an airintake throttle to increase airflow through the CAC. By opening theintake throttle, a mass airflow through the engine can be increased,thereby increasing manifold vacuum and enabling more condensate to bedrawn in. By downshifting the transmission while opening the intakethrottle, an engine speed during the deceleration can be furtherincreased, enabling the intake mass airflow to be further increased, andincreasing the amount of condensate that can be purged during thedeceleration event. In another example, when a lower gear isunavailable, condensate purging during DFSO may be initiated byincreasing airflow through the CAC by adjusting one or more of an intakethrottle, a CAC valve (shown in FIGS. 2A-B), and an intake manifoldvalve (shown in FIGS. 3A-B).

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10 for performing variousfunctions to operate engine 10, in addition to those signals previouslydiscussed, including measurement of inducted mass air flow (MAF) frommass air flow sensor 120; engine coolant temperature (ECT) fromtemperature sensor 112, shown schematically in one location within theengine 10; a profile ignition pickup signal (PIP) from Hall effectsensor 118 (or other type) coupled to crankshaft 40; the throttleposition (TP) from a throttle position sensor, as discussed; andabsolute manifold pressure signal, MAP, from sensor 122, as discussed.Engine speed signal, RPM, may be generated by controller 12 from signalPIP. Manifold pressure signal MAP from a manifold pressure sensor may beused to provide an indication of vacuum, or pressure, in the intakemanifold 44. Note that various combinations of the above sensors may beused, such as a MAF sensor without a MAP sensor, or vice versa. Duringstoichiometric operation, the MAP sensor can give an indication ofengine torque. Further, this sensor, along with the detected enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, sensor 118, which is also used as anengine speed sensor, may produce a predetermined number of equallyspaced pulses every revolution of the crankshaft 40.

Other sensors that may send signals to controller 12 include atemperature sensor 124 at the outlet of the charge air cooler 80, and aboost pressure sensor 126. Other sensors not depicted may also bepresent, such as a sensor for determining the intake air velocity at theinlet of the charge air cooler, and other sensors. In some examples,storage medium read-only memory 106 may be programmed with computerreadable data representing instructions executable by microprocessorunit 102 for performing the methods described below as well as othervariants that are anticipated but not specifically listed. Exampleroutines are described herein at FIGS. 4-6.

Turning now to FIGS. 2A and 2B, an inlet side of charge air cooler 80 isdepicted. As depicted in both FIGS. 2A and 2B, charge air cooler 80includes an operable thermal transfer area 202 configured to transferheat from inside the charge air cooler 80 to outside of the charge aircooler 80. The charge air cooler 80 includes a plurality of coolingtubes 204 located in the thermal transfer area 202 of charge air cooler80. The plurality of cooling tubes 204 are in fluidic communication withan inlet tank 206. Inlet tank 206 is configured to receive intake airvia one or more inlet passages 208 coupled to an upstream region of anintake passage (not shown in FIGS. 2A and 2B). The intake air flows fromthe inlet tank 206 to the plurality of cooling tubes 204. After passingthrough the cooling tubes 204, the intake air is routed through anoutlet tank (not shown) coupled to a downstream region of the intakepassage.

Charge air cooler 80 may also include a charge air cooler valve 210 (CACvalve) configured to change the operable thermal transfer area from afirst volume 214 (shown in FIG. 2A) comprising a relatively large areato second volume 216 (shown in FIG. 2B) comprising a relatively smallarea. CAC valve 210 may be configured as a flap, as shown. Inlet tank206 may include a divider 212 that partitions inlet tank 206 into afirst portion and a second portion. Divider 212 may include one or moreholes. FIG. 2A depicts valve 210 in an open position. When valve 210 isopen, intake air may pass through one or more holes of divider 212 suchthat intake air flows through both the first and second portions ofinlet tank 206 and through the first volume 214 of the charge air cooler80. Substantially all of the plurality of cooling tubes 204 may definethe first volume 214. In one example, the charge air cooler 80 mayinclude 21 cooling tubes, and the first volume 214 may include all 21cooling tubes.

FIG. 2B depicts valve 210 in the closed position. When closed, valve 210blocks the one or more holes of divider 212. Thus, intake air only flowsthrough the first portion of the inlet tank 206 and through the secondvolume 216 of the charge air cooler 80. A portion of the plurality ofcooling tubes 204 may define the second volume 216. The second volume216 is contained wholly within the first volume 214. That is, thecooling tubes that comprise the second volume 216 also comprise aportion of the first volume 214. Therefore, when valve 210 is closed,intake air flows through only the second volume 216, and when valve 210is open, intake air flows through the first volume 214, which containsthe second volume 216. In one example, the charge air cooler 80 mayinclude 21 cooling tubes, and the second volume 216 may include lessthan 21 cooling tubes. The second volume 216 may include less than halfthe cooling tubes that comprise the first volume 214, such as 9 coolingtubes.

CAC valve 210 may be, or may be similar to, a flapper valve. The valve210 may include a seat member (e.g., divider 212) comprising asubstantially flat stationary member having one or more holes therethrough. A closure member, for example a flap, or plate may beconfigured to move a first position spaced from the seat member therebyopening the one or more holes wherein intake air is able to flow intothe first volume 214, to a second position adjacent to the seat memberthereby closing the one or more holes wherein intake air is able to flowinto only the second volume 216.

The divider 212 may be part of the valve 210. For example, the divider212 may be a valve seat. The divider 212 may also be a dividing line ordatum, or the like, functionally dividing the charge air cooler 80 intothe two portions. Some embodiments may include two or more dividersdividing the inlet into three or more portions. In some examples one ormore configurations described herein regarding the inlet tank 206 mayinstead, or in addition, be included in an outlet tank (not shown).Substantially all of the plurality of cooling tubes 204 may be in mutualfluidic communication with the outlet tank. It will be understood thatinstead, all the tubes may be in fluid communication on the inlet sideand divided at the outlet side into two or more portions of tubes. Asimilarly configured valve may also be included in the outlet tank andfunction to control whether the fluid is allowed to pass or preventedfrom passing through a similarly configured hole.

Various embodiments may include an actuator (not illustrated) to openand to close the CAC valve 210. The actuator may be one or more of: anelectronic actuator, a vacuum controlled actuator, a mechanical pressurediaphragm, a pulse-width modulated electronic control. When the inletair is allowed to pass through all the tubes of the charge air cooler,i.e. when the valve is open, the inlet air will also experience a dropin pressure and the valve will be exposed on both sides to the pressureof the incoming inlet air. In this way the actuator may only need toprovide a motive force to open and to close the valve in order to changethe valve from an open state to a close state, but may not need toprovide force to keep the flap open or to keep the flap closed.

Thus, by modulating a position of CAC valve 210, a volume and flow rateof intake air directed through the charge air cooler can be varied. Insome embodiments, the valve may be mechanically modulated based onintake air flow, e.g., the valve flap or plate may be kept closed byspring tension that is calibrated to match air flow, such that the valveflap opens under conditions of high air flow. Thus, during low air flowconditions or low engine load conditions, the valve may be closed andthe intake air may be directed through the second (smaller) volume ofthe charge air cooler, increasing the intake air flow velocity throughthe cooler to reduce condensation accumulation. In comparison, duringhigh air flow conditions or high engine load conditions, the valve maybe opened and intake air may be directed through the first (larger)volume of the charge air cooler. In other embodiments, the valve may becontrolled by a controller, such as controller 12 of FIG. 1, based onvarious operating conditions. For example, the valve may be openedduring low condensation formation conditions and commanded closed duringconditions of high condensation formation.

In addition, as elaborated herein at FIG. 4, an intake throttle and CACvalve 210 may be opened during a condensate purging routine to increaseairflow through the CAC and thereby increase the amount of condensatepurged from the CAC to the engine intake. The purging may beadvantageously performed during a deceleration event (such as a DFSO) soas to ingest the water during conditions when cylinder combustion is notoccurring. Alternatively, to clean the condensate during thedeceleration, the CAC valve may be closed (to reduce the volume throughthe CAC) and an intake throttle opening may be increased to purge thesmaller volume. Then, once the smaller volume has been purged, the CACvalve may be opened so that both partitions of the CAC can be cleaned.Further, while the intake throttle is opened (with the CAC valve open orclosed, or in a CAC with no CAC valve), a transmission gear may bedownshifted to increase engine speed and further increase air mass flowthrough the engine the CAC. Example purging operations that can be usedfor a variable volume CAC (such as shown in FIGS. 2A-B) or anon-variable volume CAC (such as shown in FIG. 1) are described hereinwith reference to FIGS. 7-8.

Referring now to FIGS. 3A and 3B, an alternate embodiment of a chargeair cooling system is illustrated wherein the CAC includes a valvecoupled between the outlet of the CAC and the intake manifold, hereinalso referred to as an intake manifold valve. In alternate embodiments,the valve may be coupled to an inlet of the CAC. FIGS. 3A and 3B show afront perspective view of a charge air cooler system 300 including acharge air cooler 80. The charge air cooler system may be utilized todischarge water droplets from the charge air cooler which may accumulateas the result of the high ambient air humidity. This may occur, forexample, on surfaces of heat exchange passages within the charge aircooler when the surfaces are at a temperature less than the dew point ofthe ambient air entering the cooler. When condensation forms on thesecooler surfaces it may pool at a low point of the charge air cooler, forexample.

As shown, the direction of engine airflow entering charge air cooler 80is indicated generally by arrow 302, and engine airflow exiting chargeair cooler 80 is indicated generally by arrow 304. However, it will beappreciated that engine air may enter and exit charge air cooler 80 atother airflow directions and the engine airflow as indicated by arrows302 and 304 is provided as one non-limiting example. Likewise, othercharge air cooler geometries than those depicted in FIGS. 3A and 3B arepossible without departing from the scope of this disclosure.

As introduced above, engine air may enter via a first engine air passage306 upstream from charge air cooler 80. Engine air may then be cooledvia heat exchange with ambient air, indicated generally at 308, and maythen exit via a second engine air passage 310 downstream from charge aircooler 80. In other words, engine air enters at a hot side 312 of thecharge air cooler and exits at a cold side 314 of the charge air cooler(directionality of charge air flow indicated generally by arrows 309),wherein ‘hot’ and ‘cold’ indicate a relative temperature of the engineair as it passes through the charge air cooler. In this way, ambient air308 cools compressed engine air via heat exchange as the engine airpasses through the charge air cooler. However, the compressed engine airentering the charge air cooler may condense, as described above. In thissense, first engine air passage 306 may deposit condensate within thecharge air cooler.

As shown, charge air cooler 80 may include a plurality of heat exchangepassages 325 and a plurality of ambient air passages 326. Heat exchangepassages 325 may provide a conduit for charge air to be cooled byambient air cross-flow passing through the plurality of ambient airpassages 326. In this way, compressed engine air is cooled upstream fromthe combustion chambers.

Charge air cooler system 300 also includes a conduit 330 coupled to thesecond engine air passage 310. Conduit 330 leads to the intake manifold44 of the engine. Thus, conduit 330 is coupled to both charge air cooler80 and intake manifold 44. As conduit 330 is configured to deliverintake air to the engine, it may be referred to as an intake passage.Conduit 330 includes a divider 331 that portions conduit into two airflow paths, first flow path 332 and second flow path 334. Divider 331may run the entire length of conduit 330 and act as a common interiordividing wall that is shared between the first and second flow paths.Thus, conduit 330 may be fully divided the entire length from the chargeair cooler to the intake manifold, and in some embodiments, without anyintervening openings. Both air flow paths are fluidically coupled to thecharge air cooler 80 and to the intake manifold 44 such that charge airfrom the charge air cooler 80 may travel through both first flow path332 and second flow path 334 to reach the intake manifold 44. As shownin FIGS. 3A and 3B, first flow path 332 is vertically above second flowpath 334. A vertical axis 340 is depicted in FIG. 3A to illustrate therelationship between the first flow path 332 and the second flow path334. As used herein, vertical is with respect to the ground and thewheels of the vehicle in which charge air cooling system 300 isinstalled. Furthermore, as depicted in FIGS. 3A and 3B, first flow path332 has a larger cross-section diameter than second flow path 334.However, in other embodiments, second flow path 334 may have a largerdiameter, or the flow paths may have equal diameters.

First flow path 332 may be selectively opened by a valve 336 positionedacross the first flow path 332. As illustrated herein, valve 336 ispositioned at the inlet of first flow path 332 where conduit 330 iscoupled to charge air cooler 80. However, valve 336 may be positioned atother suitable locations. In one example, valve 336 may be positioned insecond flow path 334 rather than first flow path 332. In anotherexample, valve 336 may be positioned at a different location withinfirst flow path 332, such as in the middle of conduit 330, at the outletof the conduit 330, inlet of the intake manifold 44, etc.

Valve 336 may be a spring-loaded flapper valve configured to be closedunder low to mid load conditions and opened under high load conditions.For example, the spring tension acting on valve 336 may be high enoughto maintain valve 336 in a closed position when charge air velocity isrelatively low (e.g., under lower load conditions). When charge airvelocity is relatively high (e.g., under high load conditions), thehigher velocity of the charge air acting on the spring may force thevalve 336 open. FIG. 3A shows the valve 336 in the open position, withcharge air flowing to the intake manifold 44 via both first flow path332 and second flow path 334.

When closed, valve 336 may act to block first flow path 332 fromreceiving charge air, thus directing all charge air through second flowpath 334, as shown in FIG. 3B. In doing so, the velocity of charge airtraveling through the second flow path 334 increases. The increased airvelocity entrains condensate that has accumulated on the bottom surfaceof the charge air cooler 80. For example, accumulated condensate 316 maypool at a low point of charge air cooler 80, such as along the bottomsurface of charge air cooler. Accumulated condensate 316 may also poolalong surfaces of the heat exchange passages 325 and/or at collectionspoint in conduit 330 (such as bends). This condensate may be swept outof the charge air cooler under high velocity conditions, such as highload. However, during lower load conditions, the velocity of the chargeair may not be high enough to move the accumulated condensate. Byselectively closing off part of the flow path from the charge air cooler80 to the intake manifold 44 with the closed valve 336 (e.g., byselectively closing off first flow path 332), the increased velocity ofthe charge air traveling through the second flow path 334 may remove thecondensate, even during lower load conditions. During high loadconditions, when charge air velocity is higher, a closed valve 336 maypresent a large pressure drop, hindering efficient flow. Thus, valve 336is configured to open under high load conditions.

Also depicted in FIGS. 3A and 3B is a condensation collection tube 338.Condensation collection tube 338 may be coupled to the second flow path334 and include an inlet positioned near a low point of the charge aircooler 80. The condensation collection tube 338 may further narrow theflow path of charge air exiting the charge air cooler 80. In this way,condensation collection tube 338 may act as a straw to funnel charge airwith entrained condensate into the second flow path 334 and to theintake manifold 44.

It will be appreciated that the above description is non-limiting andcomponents of the charge air cooler system 200 may be of other suitablegeometric configurations than those depicted in FIGS. 3A and 3B.Additionally, it will be appreciated that features of charge air coolersystem 300 may embody configurations other than those depicted withoutdeparting from the scope of this disclosure. For example, condensationcollection tube 338 may be omitted, or it may be coupled to first flowpath 332 rather than second flow path 334. Further, while valve 336 isdepicted as a spring-loaded flapper valve configured to open or closebased on the velocity of the charge air, other valve configurations arepossible. In one example, valve 336 may be controlled by controller 12to selectively open or close based on engine operating conditions. Valve336 may be an on-off valve with a fully open and fully closed position,or it may be a continuously variable valve with a plurality ofrestriction points. Further, in alternate embodiments, the valve may becoupled to an inlet of the CAC rather than the outlet.

In another example, more than two flow paths are possible. The conduitmay contain three or more flow paths, and one or more of the flow pathsmay be controlled via a valve as described above. Alternatively, onlyone flow path may be provided, and the valve may be configured as avariable position valve that can regulate the restriction level of theopening of the flow path to change the velocity of the air travelingthrough the conduit.

As shown in FIGS. 3A and 3B, divider 331 runs the entire length ofconduit 330, from the outlet of charge air cooler 80 to in the inlet ofintake manifold 44. As such, first flow path 332 and second flow path334 share a common interior dividing wall. Further, in some embodiments,no components (other than valve 336), additional flow paths, or openingsare positioned within conduit 330, and thus first and second paths 332,334 extend from charge air cooler 80 to intake manifold 44 withoutinterruption. However, in other embodiments, additional components maybe positioned between the charge air cooler and the intake manifold,such as throttles, various sensors, another turbocharger, additionalcharge air cooler, etc. If additional components are present, theconduit between the charge air cooler and downstream component mayinclude multiple flow paths while the conduit from the downstreamcomponent to the intake manifold may only include one flow path, or theconduit from the downstream component to the intake manifold may alsoinclude multiple flow paths.

Thus, by modulating a position of intake manifold valve 336, a volumeand velocity of intake air directed through a conduit between the chargeair cooler and the intake manifold can be varied. Thus, during lowengine load conditions, the valve may be closed and the intake air maybe directed through a smaller volume of the conduit, increasing theintake air flow velocity through the cooler. In comparison, during highengine load conditions, the valve may be opened and the intake air maybe directed through a larger volume of the conduit, decreasing theintake air flow velocity through the cooler. In another embodiment, theratio of charge air cooler pressure to ambient pressure may be used inplace of engine load to control the position of intake manifold valve336. In other embodiments, the valve may be controlled by a controller,such as controller 12 of FIG. 1, based on various operating conditions.For example, the valve may be open during low condensation formationconditions and commanded closed during conditions of high condensationformation.

In addition, as elaborated herein at FIG. 4, intake manifold valve 336and an intake throttle may be opened during a condensate purging routineto increase airflow through the CAC and thereby increase the amount ofcondensate purged from the CAC to the engine intake. The purging may beadvantageously performed during a deceleration event (such as a DFSO) soas to ingest the water during conditions when cylinder combustion is notoccurring. Alternatively, to clean the condensate during thedeceleration, the intake manifold valve may be closed (to increase thevelocity of air through the CAC) and an intake throttle opening may beincreased to purge the smaller volume. Then, once the smaller volume hasbeen purged, the intake manifold valve may be opened so that bothpartitions of the CAC can be cleaned. Further, while the intake throttleis opened (with the intake manifold valve open or closed, or in a CACwith no intake manifold valve), a transmission gear may be downshifted(if a lower gear is available) to increase engine speed and furtherincrease air mass flow through the engine the CAC. Example purgingoperations that can be used for a variable volume CAC (such as shown inFIGS. 3A-B) or a non-variable volume CAC (such as shown in FIG. 1) aredescribed herein with reference to FIGS. 7-8.

It will be appreciated that while the embodiments of FIGS. 2A-B and 3A-Bshow the charge air cooler with a flapper valve, in still otherembodiments, the charge air cooler (CAC) may not have a valve coupledthereto. In those embodiments, to enable purging of condensate during adeceleration event, an air intake throttle may be opened (instead ofbeing closed) to increase airflow through the CAC. Additionally, the airintake throttle may be temporarily opened with a concomitant temporarytransmission gear downshift (such as a gear downshift used in towingmodes to increase engine braking). For example, the transmission gearmay be downshifted from a transmission third gear to a transmissionfirst gear. By opening the intake throttle and downshifting atransmission gear, a mass air flow rate though the engine and the CACmay be increased and the resulting increase in manifold vacuum can beadvantageously used during the deceleration event to draw in and purgemore condensate from the CAC. In one example, the temporary opening ofthe intake throttle during a deceleration event (such as during a DFSO)may be performed for a few seconds. As such, since the throttle openingand transmission gear downshift affects engine braking, a vehiclecontrol system may coordinate and adjust the braking efforts ofalternate vehicle brakes (e.g., wheel brakes) to maintain a desireddeceleration rate. For example, while the engine braking is temporarilyincreased, a wheel braking effort may be temporarily decreased. Asanother example, in embodiments where the engine or drive-train iscoupled to an electric machine (e.g., in a hybrid electric vehicle) orany other hybrid-like device (hydraulic or pneumatic), the throttleopening and transmission downshifting may be coordinated with suchdevices (e.g., the devices could be operated in an energy or torqueabsorbing mode) to maintain the desired deceleration rate while keepingengine speed and mass flow rate high (to continue purging the condensateduring the deceleration). Additional details on purging during a DFSO bydownshifting a transmission gear are presented at FIGS. 4 and 6.

In another embodiment, purging condensate during a DFSO by opening anintake throttle with concomitant temporary transmission gear downshiftmay also be performed with the CAC embodiments shown in FIGS. 2A-B and3A-B. By coordinating opening of the CAC or intake manifold valve withthe increased airflow from the open throttle and increased RPM fromdownshifting a transmission gear, airflow through the CAC may be furtherincreased to increase purging of condensate. In one example, during theDFSO and gear downshift, the CAC valve may be opened to increase airflowthrough the CAC and thereby increase the amount of condensate purgedfrom the CAC to the engine intake. In another example, during the DFSOand gear downshift, the intake manifold valve may be opened to increaseairflow through the CAC and provide additional condensate purging. Inthis way, the combined increase in airflow (from opening one or morevalves) and manifold vacuum (from increased RPM) may allow a largeramount of condensate to be purged from the CAC. The condensate may alsobe purged more quickly. In this way, combining increased airflow withincreased manifold vacuum may increase the efficiency of purgingcondensate form the CAC during a DFSO event.

In some embodiments, downshifting a transmission gear may be in responseto a vehicle speed. In other embodiments, downshifting a transmissiongear may be in response to vehicle speed and condensate level in a CAC.In one example, the vehicle may downshift the transmission from a firsthigher gear to a second lower gear in response to decreasing vehiclespeed during a deceleration event. In another example, during adeceleration event, the vehicle may downshift the transmission from afirst higher gear to a second lower gear in response to the condensatelevel in the CAC being above a threshold. In some cases, the second gearmay be selected based on the condensate level in the CAC. For example,the second gear may be a lower gear (with a higher gear ratio) ascondensate level in the CAC increases. In this way, downshifting to agear with a higher gear ratio may increase manifold vacuum, allowingmore condensate to be purged from the CAC. For example, downshiftingfrom a transmission fourth gear to a transmission first gear may purge agreater amount of condensate than downshifting from a transmissionfourth gear to a transmission third gear.

Selectively downshifting a transmission from a first, higher gear to asecond, lower gear during a deceleration event may be based on the firstgear (that is, the gear the transmission is already in at the time whendeceleration occurs and purging is requested) and the amount ofcondensate in the CAC. In one example, downshifting may only occur whenthe first transmission gear is above a threshold gear. Downshifting fromthis threshold gear may correspond to an increase in engine speed andairflow through the CAC necessary to purge a given amount of condensatefrom the CAC. For example, the downshifting may occur only if thetransmission is already in or above a transmission third gear (e.g., ina transmission third gear or fourth gear or fifth gear, etc.). In thisexample, downshifting from the transmission third gear to thetransmission first gear may increase engine speed to a first level. Thisfirst level may increase airflow through the CAC such that all thecondensate in the CAC is purged. If engine speed does not reach thislevel, due to the first gear being below the threshold gear, all thecondensate may not be purged from the CAC. Thus, an increase in enginespeed to purge an amount of condensate from the CAC may determine thethreshold gear for downshifting. In another example, downshifting mayonly occur if a gear difference between the first and second gear ishigher than a threshold difference. These thresholds may be based on thelowest possible gear in the given transmission configuration or thecondensate level in the CAC. For example, if the first gear which thetransmission is already in is a transmission first gear, a lower gearmay not be available and downshifting may not be possible. In this case,the threshold gear may be the transmission first gear. However, if thefirst gear the transmission is in is a transmission third gear, a lowergear may be available and downshifting may be possible. In this case,the threshold gear may be the transmission second gear and thedownshifting is enabled because the transmission is already in a gearthat is above the transmission second gear.

In another example, downshifting from a transmission fourth gear to atransmission second transmission gear may purge the condensate in theCAC. However, shifting from a transmission second gear to a transmissionfirst gear may not be enough to purge the condensate if the condensatelevel in the CAC is high. In this case, the threshold gear may be thetransmission second gear and the threshold difference may be twotransmission gears. That is, the transmission may need to be downshiftedby at least 2 gears to enable sufficient purging. In this way, thethreshold gear and/or a threshold difference (in gears) required forenabling downshifting may increase as the level of condensate in the CACincreases.

In this way, the vehicle control system may selectively downshift atransmission from a first, higher gear to a second, lower gear toincrease engine speed and increase engine airflow to purge condensatefrom a CAC. By concomitantly increasing the opening of an intakethrottle, airflow through the CAC may be further increased, increasingcondensate purging. The amount of opening of the intake throttle may bebased on the amount of downshift (e.g., difference between the first andsecond gear of the downshift) and the amount of condensate in the CAC.For example, during a larger downshift (e.g., going from a transmissionfourth to a transmission first gear) the throttle may be opened by asmaller amount to aid in purging. Alternatively, during a smallerdownshift (e.g., going from a transmission second gear to a transmissionfirst gear) the throttle may be opened by a larger amount to aid inpurging. In this way, if the condensate level in the CAC requires alarger downshift, but the gear difference between the first and secondgears is not higher than the threshold difference, condensate purgingmay still proceed by utilizing a larger throttle opening. For example,the vehicle may be in a transmission second gear while the thresholddifference (based on condensate level) is two transmission gears.Purging may proceed by opening the throttle (possibly all the way) anddownshifting from the transmission second gear to the transmission firstgear. In some cases, this may allow a similar amount of condensate to bepurged as during the larger downshift and smaller throttle opening. Inother cases, a smaller amount of condensate than the amount in the CACmay be purged. However, a smaller amount of condensate purging may beenough to decrease condensate levels in the CAC to a safer level (lesschance of engine misfire).

It will be appreciated that the purging routines described herein enablecondensate to be purged from various embodiments of a CAC to an engineintake during a deceleration event. These may include a variable volumeCAC (such as those described at FIGS. 2A-B and 3A-B) as well as otherconventional CAC embodiments, such as a non-variable volume CAC asdescribed at FIG. 1.

Now turning to FIG. 4, an example method 400 is shown for purgingcondensate from a charge air cooler to an engine intake. Byopportunistically purging during deceleration events when the engine isnot being fueled, misfire events rising from water ingestion can bereduced.

At 402, the method includes estimating and/or measuring engine operatingconditions. These may include, for example, engine speed, MAP, MAF, BP,engine temperature, catalyst temperature, ambient conditions(temperature, humidity, etc.), charge air cooler conditions (inlettemperature, outlet temperature, inlet pressure, outlet pressure, flowrate through the cooler, etc.), EGR, torque demand, etc.

At 404, the level of condensate at the CAC may be determined. This mayinclude retrieving details such as ambient air temperature, ambient airhumidity, inlet and outlet charge air temperature, inlet and outletcharge air pressure, and air mass flow rate from a plurality of sensorsand determining the amount of condensate formed in the CAC based on theretrieved data. In one example, at 406, and as further elaborated at themodel of FIG. 5, the rate of condensate formation within the CAC may bebased on ambient temperature, CAC outlet temperature, mass flow, EGR,and humidity. In another example, at 408, a condensation formation valuemay be mapped to CAC outlet temperature and a ratio of CAC pressure toambient pressure. In an alternate example, the condensation formationvalue may be mapped to CAC outlet temperature and engine load. Engineload may be a function of air mass, torque, accelerator pedal position,and throttle position, and thus may provide an indication of the airflow velocity through the CAC. For example, a moderate engine loadcombined with a relatively cool CAC outlet temperature may indicate ahigh condensation formation value, due to the cool surfaces of the CACand relatively low intake air flow velocity. The map may further includea modifier for ambient temperature.

At 410, the method includes determining if the condensate level at theCAC is higher than a threshold. As such, the threshold may correspond toan amount of condensate above which purging of the condensate isrequired to reduce misfire resulting from the slow burn rate in theengine induced by the water ingestion. If the condensate level is notabove the threshold, the routine proceeds to 412 wherein a clean-outcycle (or condensate purging routine) is not initiated. At 426, theroutine determines if there is an engine deceleration event. If there isno deceleration event, the routine ends. However, in response to anengine deceleration event, the routine includes shutting off fuelinjection to the engine cylinders, determining which gear to shift to,based on vehicle deceleration, and closing the throttle. Closing thethrottle during a deceleration event (DFSO) decreases oxygen saturationlevels in the catalyst and decreases cooling of the catalyst. Thus, whencondensate is not being purged from the CAC during a DFSO event, thethrottle may close.

Upon confirming that condensate levels are sufficiently high tonecessitate purging, at 414, the routine includes confirming if there isan engine deceleration event. In one example, the engine decelerationevent may include a tip-out (that is, where the operator has released anaccelerator pedal and requested a decrease in torque). If an enginedeceleration event is confirmed, then at 416, the routine includesshutting off fuel injection to the engine cylinders and spinning theengine un-fueled. Herein, the engine may continue to be spun via thevehicle wheels. Thus, the deceleration event includes a DFSO eventfollowing the tip-out.

At 418, the method includes determining if the condensate may be purgedfrom the CAC by shifting to a lower gear. The ability to purge byshifting to a lower gear may be based on the current transmission gearand the condensate level in the CAC. If the first gear is not higherthan a threshold gear or the difference between the first and secondgear is not higher than a threshold difference, purging by shifting to alower gear may not be possible. A method for determining this ispresented at FIG. 6. At 422, in response to the engine decelerationevent and the inability to purge by shifting to a lower gear (forexample, if the transmission is already in a gear that is lower than athreshold gear), delivery of condensate from the CAC to the engineintake may be initiated by increasing airflow through the CAC (andengine). In particular, airflow is increased while engine cylinder fuelinjection is deactivated, while the engine is spinning, and whilecylinder valves are still active. At the same time, the transmissiongear is maintained.

As one example, this may include opening a valve or flap coupled to thecharge air cooler (herein also referred to as a CAC valve) while alsoopening an intake throttle to release condensate from the CAC into theengine intake manifold. As another example, a valve or flap coupled in aconduit between the outlet (or inlet) of the charge air cooler and theengine intake manifold (herein also referred to as an intake manifoldvalve) may be opened while also opening the intake throttle to releasecondensate from the CAC into the engine intake manifold. In either case,by opening the valve, an intake manifold vacuum generated by thespinning engine may be used to draw in condensate from the CAC into theengine along the intake manifold.

In still another example, increasing the airflow to the engine and theCAC includes opening an air intake throttle (such as in embodiments of aCAC that does not have a variable volume), or increasing the opening ofan air intake throttle, to increase mass airflow rate through the CACand engine, thereby assisting in the purging of condensate to the intakemanifold. As referred to herein, the air intake throttle may refer to anintake throttle positioned in the intake manifold downstream of acompressor (such as intake throttle 21 of FIG. 1). By increasing the airflow to the engine, engine spinning may be maintained, an intakemanifold vacuum may be increased, and more condensate may be purgedduring the deceleration.

In one example, the air intake throttle may be maintained in the openposition (e.g., the fully open position) during the purging. In anotherexample, the opening of the throttle and the increasing airflow isadjusted further responsive to an amount of condensate stored in theCAC. For example, the opening of the intake throttle may be increased asthe amount of condensate in the CAC exceeds a threshold amount. Inaddition, the increasing airflow can be continued for a duration untilthe amount of condensate in the CAC is below the threshold amount. In afurther example, an opening of the throttle may be adjusted during thepurging based on an engine speed to maintain a threshold amount ofintake vacuum for the purging. Thus, as the engine speed decreasesduring the deceleration event, an opening of the intake throttle may be(further) increased to maintain the threshold vacuum. As such, once theengine speed drops below a threshold, below which further throttleadjustments may not maintain the intake manifold vacuum, throttleadjustments and further condensate purging may be discontinued.

In still further embodiments, the intake throttle may be opened duringthe deceleration event in response to the CAC condensate level beinghigher than the threshold level while the CAC valve or intake manifoldvalve is maintained closed, for a duration. For example, to clean thecondensate during the deceleration, the CAC valve may be closed toreduce the volume of the CAC, and the intake throttle opening may beincreased to increase air flow through the engine and CAC, therebyenabling purging of the smaller volume of the CAC. Then, once thesmaller volume has been sufficiently purged, with the intake throttlemaintained open, the CAC valve may be opened so that the (larger volumeof) the CAC can be completely cleaned.

As yet another example, to clean the condensate during the deceleration,the intake manifold valve may be closed to reduce the volume of aconduit coupled between the CAC and the intake manifold. In doing so,the volume of purging at the CAC is decreased and the airflow velocitythrough the conduit is increased. At the same time, the intake throttleopening may be increased to purge the smaller volume. Then, once thesmaller volume has been sufficiently purged, the intake manifold valvemay be opened so that the CAC can be completely cleaned.

In this way, while increasing the opening of the intake throttle, avalve coupled to the charge air cooler (the CAC valve or the intakemanifold valve) may be maintained closed to reduce a purge volume of thecharge air cooler. Then, after purging the reduced volume of the chargeair cooler, the valve may be opened.

Returning to 418, if the condensate may be purged by shifting to a lowergear (for example, if the transmission is already in a gear that ishigher than a threshold gear), the routine proceeds to 420. Herein, theroutine downshifts a transmission gear (e.g., from a transmission thirdgear to a transmission first gear) to increase RPM and begin purgingcondensate from the CAC. By increasing engine RPM during a DFSO event,condensate may be pulled out of the charge air cooler and into theengine, without causing misfire events. An intake manifold vacuumgenerated by the spinning engine may be increased at the higher RPM andused to draw in more condensate from the CAC into the engine along theintake manifold. The routine at 420 may also open the throttle toincrease airflow through the charge air cooler to aid in the purging. Byopening the intake throttle and downshifting a transmission gear, a massair flow rate though the engine and the CAC may be temporarily increasedduring the deceleration event to draw in and purge more condensate fromthe CAC.

In one example, the temporary opening of the intake throttle during adeceleration event (such as during a DFSO) may be performed for a fewseconds. As such, since the throttle opening and transmission geardownshift affects engine braking, a vehicle control system maycoordinate and adjust the braking efforts of alternate vehicle brakes(e.g., wheel brakes) to maintain a desired deceleration rate. As such,during a CAC purging routine that occurs during deceleration with thefuel shut off, when the intake throttle is opened to increase mass airflow rate, the vehicle may not get sufficient engine braking, andtherefore an alternate braking effort may need to be applied in order tomaintain the desired deceleration rate typically present when there isclosed throttle engine braking. For example, in embodiments where theengine or drive-train is coupled to an electric machine (e.g., in ahybrid electric vehicle) or any other hybrid-like device (hydraulic orpneumatic), the throttle opening and transmission downshifting may becoordinated with such devices (e.g., the devices could be operated in anenergy or torque absorbing mode) to maintain the desired decelerationrate while keeping engine speed and mass flow rate high (to continuepurging the condensate during the deceleration). For example, the wheelbraking torque or the motor braking torque may be increased. Afterpurging is completed, the condensate level is updated and the routineends. Additional details on purging condensate during a DFSO bydownshifting are presented at FIG. 6.

Returning to 414, if an engine deceleration event is not confirmed, theroutine proceeds to 424 to purge the condensate during acceleration orsteady-state conditions. Clean-out routines during these conditions mayinclude controlling a throttle opening and engine airflow whileadjusting engine actuators to maintain torque.

As such, by delivering condensate from a charge air cooler to an engineduring a deceleration event, the large amount of intake manifold vacuumgenerated from the engine braking can be advantageously used to drawcondensate into the engine. Further, by delivering the condensate to theengine during conditions when cylinder combustion is not occurring, thecondensate can pass through the engine system without degradingcombustion stability. Further still, since the likelihood of poorcombustion or misfire due to water ingestion is reduced by purging thecondensate while no combustion is occurring, concurrent engine actuatoradjustments for misfire control may not be required. As such, this mayenable a larger amount of condensate to be purged into the engine. Inone example, a larger amount of condensate may be purged per cycleduring the deceleration event (e.g., during a tip-out) as compared tothe amount of condensate purged per cycle during an acceleration event(e.g., during a tip-in).

In this way, during engine deceleration with fuel injection to an enginecylinder deactivated, airflow through a charge air cooler can beincreased based on an amount of condensate stored in the charge aircooler. By increasing airflow through the engine during a decelerationwhen the amount of condensate stored in the charge air cooler is higher,a large amount of condensate can be advantageously drawn in to theintake manifold during non-combustion cylinder conditions enablingpurging to be accomplished with reduce risk of misfires. In comparison,during a deceleration when the amount of condensate stored in the chargeair cooler is lower, airflow through the engine may be decreased.

FIG. 5 illustrates a method 500 for estimating the amount of condensatestored within a CAC. Based on the amount of condensate at the CACrelative to a threshold value, condensate purging routines, such asthose discussed at FIG. 4, may be initiated.

The method begins at 502 by determining the engine operating conditions.These may include, as elaborated previously at 402, ambient conditions,CAC conditions (inlet and outlet temperatures and pressures, flow ratethrough the CAC, etc.), mass air flow, MAP, EGR flow, engine speed andload, engine temperature, boost, etc. Next, at 504, the routinedetermines if the ambient humidity is known. In one example, the ambienthumidity may be known based on the output of a humidity sensor coupledto the engine. In another example, humidity may be inferred from adownstream UEGO sensor or obtained from infotronics (e.g., internetconnections, a vehicle navigation system, etc.) or a rain/wiper sensorsignal. If the humidity is not known (for example, if the engine doesnot include a humidity sensor), the humidity may be set to 100% at 506.However, if the humidity is known, the known humidity value, as providedby the humidity sensor, may be used as the humidity setting at 508.

The ambient temperature and humidity may be used to determine the dewpoint of the intake air, which may be further affected by the amount ofEGR in the intake air (e.g., EGR may have a different humidity andtemperature than the air from the atmosphere). The difference betweenthe dew point and the CAC outlet temperature indicates whethercondensation will form within the cooler, and the mass air flow mayaffect how much condensation actually accumulates within the cooler. At510, an algorithm may calculate the saturation vapor pressure at the CACoutlet as a function of the CAC outlet temperature and pressure. Thealgorithm then calculates the mass of water at this saturation vaporpressure at 512. Finally, the condensation formation rate at the CACoutlet is determined at 514 by subtracting the mass of water at thesaturation vapor pressure condition at the CAC outlet from the mass ofwater in the ambient air. By determining the amount of time betweencondensate measurements at 516, method 500 may determine the amount ofcondensate within the CAC since a last measurement at 518. The currentcondensate amount in the CAC is calculated at 522 by adding thecondensate value estimated at 518 to the previous condensate value andthen subtracting any condensate losses since the last routine (that is,an amount of condensate removed. for example, via purging routines) at520. Condensate losses may be assumed to be zero if the CAC outlettemperature was above the dew point. Alternatively, at 520, the amountof condensate removed may be modeled or determined empirically as afunction of air mass and integrated down with each software task loop(that is, with each run of routine 500).

As such, the method of FIG. 5 may be used by the controller during theroutine of FIG. 4 to use a modeling method for estimating the amount ofcondensate at the CAC. In alternate embodiments, the engine controlsystem may use a mapping method to map the amount of condensate at theCAC to a CAC inlet/outlet temperature, an ambient humidity, and anengine load. For example, the values may be mapped and stored in alook-up table that is retrieved by the controller during the routine ofFIG. 4 (at 408), and updated thereafter.

Turning now to FIG. 6, an example method 600 is shown for purgingcondensate from a CAC to an engine intake during a deceleration event bydownshifting a transmission from a first, higher gear to a second, lowergear. By downshifting a transmission gear, opening an air intakethrottle, and possibly opening a CAC valve or an intake manifold valve,a larger amount of condensate may be purged from the CAC.

At 602, the method includes estimating and/or measuring engine operatingconditions. These may include, for example, engine speed, MAP, MAF, BP,engine temperature, catalyst temperature, ambient conditions(temperature, humidity, etc.), CAC conditions (inlet temperature, outlettemperature, inlet pressure, outlet pressure, flow rate through thecooler, etc.), EGR, torque demand, transmission conditions (currenttransmission gear, presence of engine breaking, etc.), etc.

At 603, the routine determines the required downshift based on CACcondensate level. This may include determining a threshold gear for thefirst, higher transmission gear. Specifically, the first gear may needto be at or above the threshold gear to purge an amount of condensate.The method at 603 may also include determining a threshold differencebetween the first and second gear. Specifically, the difference betweenthe first and second gear may need to be at or higher than a thresholddifference to purge an amount of condensate. Thus, these thresholds maybe based on the amount of condensate in the CAC. For example, if thereis a large amount of condensate in the CAC, a larger downshift (orhigher threshold difference between the first and second gear) may berequired. This larger downshift may involve skipping gears (e.g., goingfrom a third to a first gear). In another example, a smaller amount ofcondensate in the CAC may require a smaller downshift (e.g.,downshifting from a second to a first transmission gear). As such, themethod may include skipping gears to a greater or lesser degree inresponse to the amount of condensate in the CAC.

At 604, the routine determines if the required downshift determined at603 is possible. For example, if the vehicle is in a transmission thirdgear and the threshold difference is two transmission gears, the methodmay proceed to 606. However, if the vehicle is in a transmission secondgear, purging by downshifting may not be possible. If the requireddownshift is not possible, the routine continues to 608 where thetransmission gear is maintained and CAC condensate purging is initiated.Delivery of condensate from the CAC to the engine intake manifold may beinitiated by opening an air intake throttle and possibly opening a CACvalve or an intake manifold valve (as described above with reference to422 in method 400). In other embodiments, the method at 608 may includeopening the throttle and downshifting to a lower gear if one isavailable, even if the required thresholds were not met at 604. In thisway, the smaller gear downshift may still increase manifold vacuum and,along with increased airflow from the open throttle, purge condensatefrom the CAC. Further, the throttle opening may be increased tocompensate for the smaller gear downshift.

Alternatively at 604, if the required downshift is possible, the routinecontinues on to 606 to confirm if there is engine braking. As describedabove, engine braking may be used to aid in slowing down the vehicleduring a deceleration event. If engine braking is required, the routinechecks at 610 if there is a lower gear available which may continue toprovide the required engine braking. If the lower gear with enginebraking is confirmed, condensate purging is initiated by downshifting atransmission gear at 612 to increase RPM. As the engine spins faster,condensate is drawn from the CAC into the engine. An intake throttle mayalso open at 612 to increase airflow through the CAC and increase theamount of condensate purged. Increased airflow to the engine, responsiveto increasing throttle opening, may decrease engine braking. Therefore,the routine at 614 may adjust alternate vehicle brakes (e.g., wheelbrakes) to maintain the required braking level. For example, if throttleopening decreases engine braking to a level less than required,increasing wheel brakes by a proportional amount may allow the vehicleto maintain the same level of braking. In another example, where theengine or drive-train is coupled to an electric machine (e.g., in ahybrid electric vehicle) or any other hybrid-like device (hydraulic orpneumatic), the devices could be operated in an energy or torqueabsorbing mode to maintain the desired deceleration rate while keepingengine speed and mass flow rate high (to continue purging the condensateduring the deceleration).

Next at 616, it may be determined if the condensate level has dropped tobelow the threshold level. That is, it may be determined if the CAC hasbeen sufficiently purged. If yes, then at 620, the routine includesstopping purging of condensate from the CAC to the intake manifold byclosing vales used for purging (the CAC valve and/or the intake manifoldvalve). The downshifted transmission gear and intake throttle may alsobe adjusted back to their requested positions. After completing thepurging, the condensate level at the CAC may be updated. Else, if thecondensate level has not dropped below the threshold level, the routinemay continue purging condensate to the engine intake manifold at 618.

It will be appreciated that in further embodiments, the purging duringthe deceleration event may also be stopped in response to a resuming ofengine cylinder fueling. For example, in response to a sudden increasein torque demand (e.g., a tip-in, or the vehicle reaching an uphillsegment), cylinder fueling may be resumed and the purging during a DFSOevent may be stopped. In one example, if purging has not been completedand the vehicle driver tips in, further purging may be discontinued. Thecontroller may initiate an alternate purging routine to enablecompletion of condensate purging during an engine acceleration event, aselaborated above. Alternatively, if the engine speed drops below athreshold speed during the deceleration (e.g., due to a correspondingdrop in vehicle speed), such that insufficient manifold vacuum isavailable for purging the condensate, the CAC valve or intake manifoldvalve may be closed to stop purging condensate. In one example, ifpurging has not been completed and the engine has spun to rest, furtherpurging may be discontinued. In still a further embodiment, as theengine speed changes (e.g., decreases) during the deceleration, theintake throttle opening may be adjusted (e.g., increased) to maintain athreshold amount of intake manifold vacuum for the purging operation.Then, when throttle adjustments cannot be used to provide the thresholdintake manifold vacuum, the purging may be stopped. As an example, theincreasing airflow may be continued for a duration until an earlier ofthe amount of condensate in the charge air cooler is below the thresholdand fuel injection to the deactivated cylinder is resumed. In each case,after stopping the purging, the condensate level at the CAC may beupdated. Alternatively, the CAC level can be updated as the purginghappens. For example, the controller may characterize the mass of waterpurged as a function of the air mass flow rate. Then, at each executionof the software task loop (the purging routine), the water level can beintegrated down by the amount cleansed. A hysteresis may be added to thepurge cycle threshold so that the routine is not exited until adequatepurging has been performed.

In this way, purging condensate during a deceleration event bydownshifting a transmission from a first, higher gear to a second, lowergear may proceed when the first transmission gear is above a thresholdgear and/or when the gear difference between the first and second gearis higher than a threshold difference. In a first example, thecondensate level in the CAC may be high, requiring a larger geardownshift. In this case, the gear threshold difference may be set attwo. If the vehicle is in the transmission fourth gear, the transmissionmay be downshifted to the transmission second gear to purge condensate.Alternatively, the controller may downshift the transmission from thetransmission fourth gear to the transmission first gear to purgecondensate at a faster rate. However, if the vehicle is in thetransmission second gear, the required gear downshift of two gears isnot met. Thus, purging by downshifting may not be possible. However, thecontroller may increase throttle opening and downshift the transmissionfrom the transmission second to transmission first gear to purge asmaller amount of condensate. In another example, the throttle openingmay be increased along with the smaller gear downshift in order to purgea larger amount of condensate. In this way, throttle opening anddownshifting may be coordinated to increase manifold vacuum sufficientlyduring the deceleration to purge the CAC condensate.

In a second example, the condensate level in the CAC may be lower (butstill above a threshold to initiate purging during a decelerationevent), requiring a smaller gear downshift to purge the condensate. Inthis case, the gear threshold difference may be set to one and the gearthreshold may be set to the transmission first gear. If the vehicle isin the transmission third gear, the controller may downshift to thetransmission second gear to purge condensate. Alternatively, thecontroller may downshift from the transmission third gear to thetransmission first gear to increase the rate of condensate purging.Determining which gear to shift to may depend on other engine operatingconditions, such as rate of vehicle deceleration and engine brakingrequirements. For example, if increased engine braking is needed, thecontroller may downshift from the transmission third gear to thetransmission first gear to increase engine braking and condensatepurging. Returning to the second example, if the vehicle is instead inthe transmission first gear, condensate may not be purged bydownshifting. Since the vehicle is in the transmission first gear, alower gear is not available. Thus, downshifting is not possible andcondensate purging may be initiated by opening the throttle.

Now turning to FIG. 7, graph 700 shows an example condensate purgingoperation during acceleration and deceleration events. Specifically,graph 700 shows a change in pedal position (PP) indicative of anoperator torque demand at plot 702, a corresponding change in vehiclespeed is shown at plot 704, and a corresponding change in engine speed(Ne or RPM) is shown at plot 706. Plot 707 depicts a change in enginemass fuel. A change in transmission gear is shown at plot 714 where 4 isthe highest available gear and 1 is the lowest available gear. Further,changes to a CAC condensate level are shown at plot 708, changes to anair intake throttle position are shown at plot 710, and changes to theposition of a CAC valve of the CAC are shown at plot 712. While plot 712of the depicted example is shown with reference to a CAC valve, such asthe valve of FIGS. 2A-B, in an alternate embodiment, the sameadjustments may be performed with reference to an intake manifold valve,such as the valve of FIGS. 3A-B. Further, the same operations may beperformed in embodiments of a CAC not including a valve for varying avolume of the CAC.

Prior to t1, a vehicle operator may have applied the accelerator pedalto request torque and vehicle speed (plot 706). Accordingly, a pedalposition may be higher than a threshold (plot 702), and an engine speedmay be elevated to provide the desired torque (plot 704) and desiredvehicle speed. Additionally, the vehicle may begin in a transmissiongear 3 (714). During this time, in response to the engine load beinghigher than a threshold, a CAC valve may be opened to allow air to flowthrough the CAC. However, even with the CAC valve open, condensate levelmay be gradually increasing (plot 708) and shortly before t1, thecondensate level may increase above threshold level 709, indicating aneed for CAC condensate purging.

At t1, a tip-out event may occur, as indicated by the drop in pedalposition. In response to the tip-out, the intake air throttle openingmay be initially decreased (or closed) to reduce air flow through theengine. The engine speed may track the vehicle speed. In response to thedrop in engine load, the CAC valve may be closed to reduce airflowthrough the CAC. At t2, the vehicle may start decelerating. In responseto the reduced torque demand during the deceleration, fuel injection toengine cylinders may be shut off. That is, a deceleration fuel shut off(DFSO) operation may be performed. Due to the DFSO event, an engine fuelmass may decrease (708). Also, as a result of the DFSO event, enginebraking may be enabled.

As such, in response to the deceleration event, intake airflow may bereduced and maintained at the reduced level until increased torque issubsequently demanded by the vehicle operator (e.g., due to a tip-infollowing the deceleration event). However, in the present example, inresponse to the condensate level being higher than the threshold duringthe DFSO event, at t2, condensate may be purged from the CAC. In thisexample, the vehicle is in transmission gear 1 at t2 (714). Thus, sincea lower gear is not available, condensate purging may be initiated byincreasing airflow through the CAC. An opening of the intake throttlemay be increased (e.g., the throttle may be fully opened) while the CACvalve is closed to enable purging of the condensate from the CAC intothe engine intake. In particular, by closing the CAC valve, a volume ofthe CAC is decreased while at the same time, by opening the intakethrottle, an airflow through the engine and the CAC is increased. Thisallows condensate stored in the smaller volume of the CAC to be rapidlypurged between t2 and t3 (e.g., in a couple of seconds). At t3, oncepurging of the smaller volume of the CAC is completed, the CAC valve maybe opened while the intake throttle is maintained open to allow the restof the CAC to be purged during the DFSO event. At t4, purging of the CACmay be considered complete in response to the condensate level beingbelow the threshold level. In response to the purging being completedwhile deceleration conditions are still present, the intake throttle maybe closed to reduce airflow. In addition, the CAC valve may be closed toreduce airflow through the CAC during the low load condition.

In this way, during the deceleration event, the CAC valve may be openedand closed, with the opening and closing of the CAC valve based at leaston the amount of condensate in the charge air cooler (and independent ofthe engine load). In addition, since the purging occurs while nocylinder combustion is occurring, concomitant engine actuatoradjustments required for misfire control are not required. For example,a spark timing may be maintained. It will be appreciated that while theexample in the depicted figure shows the throttle maintained openbetween t2 and t4, in alternate embodiments, an opening of the throttlemay be dynamically adjusted between t2 and t4 based on the change inengine speed to maintain an amount of intake manifold vacuum forsufficient purging of condensate from the CAC into the engine intake.

At t5, the vehicle operator may tip-in, as indicated by the suddenincrease in pedal position. In response to the tip-in, the intakethrottle may be opened to provide the desired airflow and meet thetorque demand. In addition, an engine speed, vehicle speed, andtransmission gear may increase. As such, during an acceleration event,an opening and closing of the CAC valve is based on the engine load.Therefore, in response to the high load condition at the tip-in, the CACvalve may be reopened. While the valve is open, the increased airflow ofthe tip-in can be advantageously used to purge at least some condensatefrom the CAC (or reduce accumulation of condensate at the CAC), eventhough condensate levels at the CAC are not sufficiently high to need anactive purging routine.

A second later tip-in occurring after an amount of time has elapsed isshown at t6. Herein, during the second later tip-in, the condensatelevels at the CAC may be sufficiently high and an active purging routinemay be requested. Herein, in response to the tip-in, the intake throttleopening may be increased to provide increased airflow. The increasedairflow may then be advantageously used to purge condensate from the CACto the intake. In particular, the CAC valve may be opened while thethrottle is open to rapidly purge the stored condensate. In addition,one or more alternate engine operating parameters (not shown) may beadjusted to maintain the desired torque. For example, while thecondensate is being purged to the intake during the tip-in, a sparkignition timing may be advanced, or an amount of retard may be limited.In one example, the controller may meter the amount of ingested water bylimiting or shaping the response of the air mass inducted curve. A sparktiming adjustment may then be used to maintain combustion timing (e.g.,to avoid late burns).

A second later tip-out occurring after another amount of time haselapsed is shown at t7. Herein, during the second later tip-out, thecondensate levels at the CAC (708) may be below a threshold level 709such that no clean-out cycle is initiated. In response to the tip-out,the air intake throttle opening may be closed (710). The vehicle maybegin decelerating at t8 (704) and fuel injection to engine cylindersmay be shut off That is, a deceleration fuel shut off (DFSO) operationmay be performed. Due to the DFSO event, an engine fuel mass maydecrease (708). Also, as a result of the DFSO event, a transmission gearmay be downshifted from transmission gear 3 to transmission gear 2 andengine braking may be enabled.

Thus, during a first condition, as shown at t6, when intake air flow ishigher than a threshold flow, condensate is delivered from a charge aircooler to an engine during an engine acceleration event. Then, during asecond condition, as shown at t2, when intake vacuum is higher than athreshold vacuum, condensate is delivered from the charge air cooler tothe engine during an engine deceleration event. Herein during the firstcondition, a first smaller (net) amount of condensate is delivered andduring the second condition, a second larger (net) amount of condensateis delivered to the engine intake. Further, during the first condition,fuel is injected to engine cylinders during the delivering of condensatewhile during the second condition, fuel is not injected to enginecylinders during the delivering. Further, during the first condition, anintake throttle opening is increased based on a pedal position toincrease air flow, while during the second condition, the intakethrottle opening is increased based on a condensate level at the chargeair cooler, the inability to shift to a lower gear, and an engine speedto increase intake manifold vacuum. Likewise, during the firstcondition, opening of a valve coupled to the charge air cooler is basedon an engine load, while during the second condition, opening of thevalve coupled to the charge air cooler is based on a condensate level atthe charge air cooler. Further still, during the first condition, sparkignition timing is advanced while during the second condition, sparkignition timing is maintained.

A third condition, wherein condensate is purged from the CAC in responseto a deceleration event and the ability to shift to a lower gear, isshown at FIG. 8. Graph 800 illustrates an example of purging condensatefrom a CAC, during a deceleration event, by downshifting a transmissiongear and opening an intake throttle to increase engine speed (Ne or RPM)and draw condensate into the intake manifold.

Specifically, graph 800 shows a change in pedal position (PP) indicativeof an operator torque demand at plot 802, a corresponding change invehicle speed is shown at plot 804, and a corresponding change in enginespeed (Ne or RPM) is shown at plot 806. A change in transmission gear isshown at plot 814 where 4 is the highest available gear and 1 is thelowest available gear. Plot 807 depicts a change in engine mass fuel.Further, changes to a CAC condensate level (CL) are shown at plot 808,changes to an air intake throttle position are shown at plot 810, andchanges to the position of a CAC valve of the CAC are shown at plot 812.While plot 712 of the depicted example is shown with reference to a CACvalve, such as the valve of FIGS. 2A-B, in an alternate embodiment, thesame adjustments may be performed with reference to an intake manifoldvalve, such as the valve of FIGS. 3A-B. Alternatively, example 800 mayproceed without CAC valve or intake manifold valve adjustments if theCAC is not equipped with these valves. Further, graph 800 shows changesin engine braking at plot 816 and changes to alternate vehicle brakes(e.g., wheel brakes).

As in FIG. 7, prior to t11, a vehicle operator may have applied theaccelerator pedal to request torque and vehicle speed (plot 806).Accordingly, a pedal position may be higher than a threshold (plot 802),and an engine speed may be elevated to provide the desired torque (plot804) and desired vehicle speed. Additionally, the vehicle may begin in atransmission gear 3 (814), without applying wheel brakes (818) orengaging engine braking (816). During this time, in response to theengine load being higher than a threshold, a CAC valve may be opened toallow air to flow through the CAC. However, even with the CAC valveopen, condensate level may be gradually increasing (plot 808) andshortly before t11, the condensate level may increase above thresholdlevel 809, indicating a need for CAC condensate purging.

At t11, a tip-out event may occur, as indicated by the drop in pedalposition (802). In response to the tip-out, the intake air throttleopening may be initially decreased (or closed) to reduce air flowthrough the engine. The engine speed may track the vehicle speed. Inresponse to the drop in engine load, the CAC valve may be closed toreduce airflow through the CAC. At t12, the vehicle may startdecelerating. In response to the reduced torque demand during thedeceleration, fuel injection to engine cylinders may be shut off. Thatis, a deceleration fuel shut off (DFSO) operation may be performed. Dueto the DFSO event, an engine fuel mass may decrease (plot 807). Also, asa result of the DFSO event, engine braking may be enabled (816).

As such, in response to the deceleration event, intake airflow may bereduced and maintained at the reduced level until increased torque issubsequently demanded by the vehicle operator (e.g., due to a tip-infollowing the deceleration event). However, in the present example, inresponse to the condensate level being higher than the threshold duringthe DFSO event, at t2, condensate may be purged from the CAC. In thisexample, the vehicle is in transmission gear 3 at t2 (814). In thisexample, the threshold difference for the gear downshift may be set atone, based on the amount of condensate in the CAC. Thus, since thedifference between the first (transmission gear 3) and second(transmission gear 1) gear is higher than the threshold difference,condensate purging may be initiated by shifting from transmission gear 3to transmission gear 1. In this way, by shifting from a higher to alower transmission gear, engine speed increases (806) and manifoldvacuum increases, pulling condensate from the CAC to the intakemanifold. In some embodiments, the throttle opening may be increasedwhile a transmission gear is downshifted to further increase airflowthrough the engine and CAC, thereby increasing purging efficiency (810).The increased throttle opening may decrease engine braking. As such,between t12 and t14 of the deceleration event, when engine braking isused to slow the vehicle, alternate vehicle braking efforts may beadjusted to maintain a desired deceleration rate. For example, a vehiclecontrol system may coordinate and adjust the braking efforts ofalternate vehicle brakes (e.g., wheel brakes) to maintain the desireddeceleration rate. Specifically, as shown in graph 800, wheel brakingeffort may be increased (818) at t13 to compensate for decreased enginebraking (816). In alternate embodiments, other torque-absorbing meansmay be used additionally or alternatively to wheel brakes to compensatefor decreased engine braking. For example, in embodiments where theengine or drive-train is coupled to an electric machine (e.g., in ahybrid electric vehicle) or any other hybrid-like device (hydraulic orpneumatic), the devices could be operated in an energy or torqueabsorbing mode to maintain the desired deceleration rate while keepingengine speed and mass flow rate high (to continue purging the condensateduring the deceleration).

While the opening of the intake throttle is increased at t12, the CACvalve may be closed to enable purging of the condensate stored in asmaller volume of the CAC. At t13, once purging of the smaller volume ofthe CAC is completed, the CAC valve may be opened while the intakethrottle is maintained open to allow the rest of the CAC to be purgedduring the DFSO event. At t14, purging of the CAC may be consideredcomplete in response to the condensate level being below the thresholdlevel. In response to the purging being completed while decelerationconditions are still present, the intake throttle may be closed toreduce airflow. As a result, wheel brakes may be reduced (818) at t14since engine braking may no longer be reduced by throttle opening. Inaddition, the CAC valve may be closed to reduce airflow through the CACduring the low load condition. At t15, the vehicle operator may tip-in,as indicated by the sudden increase in pedal position and any brakingmay be stopped. In response to the tip-in, the intake throttle may beopened to provide the desired airflow and meet the torque demand. Inaddition, an engine speed, vehicle speed, and transmission gear mayincrease.

At t16, condensate level in the CAC increases above threshold level 809.At t17, a tip-out event may occur again, as indicated by the drop inpedal position (802). In response to the tip-out, the intake airthrottle opening may initially decrease (or close) to reduce air flowthrough the engine. At t18, the vehicle may start decelerating and fuelinjection to engine cylinders may be shut off Due to the DFSO event, anengine fuel mass may decrease (plot 807). Also, as a result of the DFSOevent, engine braking may be enabled (816).

In this example, the vehicle is in transmission gear 2 at t18 (814).Since condensate level is higher at t18 than it was at t12, thethreshold difference for the gear downshift may be set higher at two(vs. one in the example at t12). Thus, since the difference between thefirst (2^(nd)) and second (1^(st)) gear is lower than the thresholddifference, condensate purging may be initiated by increasing throttleopening at t18 (810). Even though the gear difference is lower than thethreshold, the vehicle may still downshift from the transmission gear 2to transmission gear 1 at t18. This smaller downshift may increaseengine speed (806). However, the increase is less than the example att12, during the larger downshift. Throttle opening at t18 may be greaterthan at t12 to compensate for the smaller gear shift and the largeramount of condensate. In this way, by performing a smaller gear shiftwhile increasing throttle opening to a greater level, condensate may bepurged from the CAC to the intake manifold. Due to a smaller geardownshift, condensate may purge more slowly at t18 than at t12.

Thus, condensate may be delivered from a CAC to an engine during anengine deceleration event. During a second condition, as shown at t2 ingraph 700, condensate purging is initiated by increasing airflow throughthe CAC by increasing the opening of a throttle. Alternatively, during athird condition, as shown at t12 in graph 800, condensate purging isinitiated by downshifting a transmission gear and increasing enginespeed (RPM). A throttle opening may also be increased to increaseairflow through the CAC. During the third condition (t12 to t14), enginespeed increases to a higher RPM level than during the second condition(t2 to t4). This may allow a larger (net) amount of condensate to bedelivered to the engine intake in a shorter period of time. For example,the duration of condensate purging between t2 and t4 in graph 700 may belonger than the duration of condensate purging between 12 and t14 ingraph 800. Thus, condensate purging may be more efficient during adeceleration event when downshifting a transmission gear is used inconjunction with increasing throttle opening.

In this way, condensate stored in a CAC can be purged to an engineintake during a deceleration event. By downshifting a transmission gear,while increasing airflow through the engine intake manifold and the CACduring the deceleration event, misfires occurring due to ingestion ofwater into an engine and a resulting slow burn can be reduced. Inparticular, by drawing in the condensate during conditions when enginecylinders are not combusting, misfires as well as issues related todegraded combustion stability are reduced. Additionally, by downshiftinga transmission gear, purging efficiency may be increased while utilizingthe increased manifold vacuum. Further, concurrent engine actuatoradjustments otherwise needed for misfire control may not be required. Assuch, this allows a larger amount of condensate to be purged into theengine without increasing engine misfires.

Note that the example control routines included herein can be used withvarious engine and/or vehicle system configurations. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. Further, one or moreof the various system configurations may be used in combination with oneor more of the described diagnostic routines. The subject matter of thepresent disclosure includes all novel and non-obvious combinations andsub-combinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The invention claimed is:
 1. A method for a boosted engine, comprising:during a deceleration event while engine cylinder fuel injection isdeactivated, while the engine is spinning, and while cylinder valves arestill active, selectively downshifting an automatic transmission havinga clutch from a first, higher gear to a second, lower gear to increaseengine speed and increase engine airflow in response to a condensatelevel in a charge air cooler.
 2. The method of claim 1, wherein theengine is a turbocharged engine having direct fuel injection.
 3. Themethod of claim 2, further comprising, during the deceleration event,increasing an opening of an intake throttle to increase airflow throughthe charge air cooler.
 4. The method of claim 3, wherein the increasingairflow and downshifting the transmission is continued for a durationuntil an amount of condensate in the charge air cooler is below athreshold.
 5. The method of claim 3, wherein the opening of the intakethrottle increases as the engine speed decreases during the decelerationevent to maintain a threshold vacuum.
 6. The method of claim 1, whereinselectively downshifting during the deceleration event includesdownshifting the transmission if a gear difference between the first andsecond gear is higher than a threshold difference.
 7. The method ofclaim 6, wherein selectively downshifting further includes increasing anopening of an intake throttle to increase airflow through the charge aircooler and not downshifting the transmission if the gear differencebetween the first and second gear is lower than the thresholddifference.
 8. The method of claim 3, wherein increasing airflow througha charge air cooler includes decreasing engine braking.
 9. The method ofclaim 8, wherein the engine is coupled to a vehicle, the method furthercomprising: adjusting an amount of wheel braking during the increasingairflow to maintain a vehicle deceleration rate.
 10. The method of claim8, wherein the engine is coupled to a hybrid electric vehicle, themethod further comprising, during the increasing airflow, operating anelectric machine of the hybrid electric vehicle in a torque-absorbingmode to maintain a vehicle deceleration rate.
 11. The method of claim 1,wherein the deceleration event includes a tip-out.
 12. A vehicle enginemethod, comprising: in response to a condensate level in a charge aircooler and during conditions when engine direct injection fueling isselectively deactivated and a transmission gear is above a thresholdgear, downshifting the transmission gear to increase engine speed andopening a throttle to increase airflow through a charge air cooler. 13.The method of claim 12, wherein the engine is a turbocharged engine. 14.The method of claim 13, wherein the increasing airflow and downshiftingthe transmission gear is continued for a duration until an amount ofcondensate in the charge air cooler is below a threshold.
 15. The methodof claim 13, wherein the downshifting the transmission gear includesdownshifting a transmission from a first higher gear to a second lowergear, wherein the second gear is selected based on the condensate levelin the charge air cooler.
 16. The method of claim 15, wherein the secondgear has a higher gear ratio as the condensate level increases.
 17. Themethod of claim 13, wherein the vehicle is a hybrid electric vehicle,the method further comprising, during the increasing airflow, increasingone or more of a wheel brake torque and motor torque to maintain avehicle deceleration rate, the increasing based on the throttle opening.18. An engine method, comprising: during a first condition when anautomatic transmission having a clutch is in a first transmission gearthat is higher than a threshold gear, delivering condensate from acharge air cooler to an engine intake manifold by downshifting atransmission gear to a second transmission gear that is lower than thefirst transmission gear and opening an air intake throttle; and during asecond condition when the transmission in a third transmission gear thatis lower than the threshold gear, delivering condensate from the chargeair cooler to the engine intake manifold by maintaining the transmissiongear while opening the air intake throttle.
 19. The method of claim 18,wherein the engine is a turbocharged direct injection engine.
 20. Themethod of claim 19, wherein the threshold gear is based on an amount ofcondensate in the charge air cooler and wherein increasing airflowthrough the charge air cooler further includes opening one of a valvecoupled to the charge air cooler and a valve coupled between an outletor inlet of the charge air cooler and an engine intake manifold.